This disclosure relates to a method and apparatus for treating a subterranean well formation to stimulate the production of hydrocarbons and, more particularly, such a method and apparatus utilizing foam diversion in the well formation.
Several techniques have evolved for treating a subterranean well formation to stimulate hydrocarbon production. For example, hydraulic fracture acidizing methods have often been used according to which a portion of a formation to be stimulated is isolated using conventional packers, or the like, and a stimulation fluid containing gels, acids, sand slurry, and the like, is pumped through the well bore into the isolated portion of the formation. The pressurized stimulation fluid pushes against the formation at a very high force to establish and extend cracks on the formation.
Also, squeezing methods have been used which involve introducing stimulation fluids containing acids to formations at a pressure that is higher than the formation pressure (but not as high as the fluid pressure in the fracturing methods), causing the fluid to infiltrate the pores in the formation and react with the formation to enlarge the pores.
In these methods, foam diversion is often used according to which foam is created and used to plug pores in the formation and thus promote the spreading of the fluids over a relatively large surface area of the formation. To this end, conventional foaming equipment is provided on the ground surface that creates a foam, which is then pumped downhole. Foams, however, have much larger friction coefficients and reduced hydrostatic effects, both of which severely increase the required pressures to treat the well. Moreover, using conventional procedures, a foam generated at the surface is sent through the same conduit as the other liquids. Therefore, if a foam is needed, it cannot be introduced into the formation until all the liquids used previously are cleared from the wellbore. The gas into the foam generator could be changed, but this change will not occur until all previously delivered foam clears the wellbore. This, of course, is very time-consuming.
According to an embodiment of the present invention a method for acid treatment of a subterranean well formation is provided to stimulate the production of hydrocarbons which utilizes foam diversion which can be initiated substantially instantaneously in situ.